1. Field of the Invention
The present invention relates to a noise silencer for reducing noise generated in an intake system of a vehicle engine.
2. Related Art
FIG. 14 shows a conventional intake system of a vehicle engine. The intake system has an air cleaner 100, an intake pipe 105 disposed at an upstream air side of the air cleaner 100, an intake pipe 106 disposed at a downstream air side of the air cleaner 100 and a throttle body 101 disposed at a downstream air side of the intake pipe 106. Air is sucked into and flows through the intake pipe 105, the air cleaner 100, the intake pipe 106 and the throttle body 101, and is introduced into each cylinder of an engine 103 through a surge tank 104 and an intake manifold 102. A resonator 107 is attached to the intake pipe 105 and resonators 109, 110 are attached to the intake pipe 106.
In the intake system, noise is generated by negative pressure caused by opening and closing of an intake valve, and is transmitted from the engine 103 to the intake pipe 105. For a 4-cylinder engine, frequency of generated noise is generally 1 kHz or less. That is, generated noise may have frequency such as 100, 200 and 400 Hz with relatively high sound pressure. Hereinafter, frequency level such as a high frequency or a low frequency is a level determined within the frequency of noise generated in the intake system being 1 kHz or less.
The capacity and mounting position of each of the resonators 107, 109 and 110 are adjusted so that each of the resonators 107, 109 and 110 reduce noise having a different frequency. The resonators 107, 109 and 110 respectively reduce noise having a frequency 100, 400 and 200 Hz. Thus, whole noise generated in the intake system is reduced by the resonators 107, 109 and 110.
However, each of the resonators 107, 109 and 110 has a structure for reducing noise in a relatively narrow frequency range. Therefore, a resonator may be required for each 20 frequency range of noise. However, recently, the intake system needs to be compact, and the air cleaner 100 and the throttle body 101 may be directly connected with each other without an intake pipe 106 therebetween. In such a case, the attachment space for the resonators 109, 110 is eliminated, thereby making it difficult to attach several resonators to the intake system corresponding to frequency ranges of noise. Further, the size of a resonator for reducing low-frequency noise is relatively large. Therefore, when the resonator for reducing low-frequency noise is attached to the intake pipe, the size of the intake pipe itself is increased.
JP-A-5-187336 discloses a noise silencer in which noise generated in an intake system of a vehicle engine is reflected by a concave reflection surface and is sent back to an intake side of the engine so that noise in the intake system is reduced.
However, since low-frequency noise may not be sufficiently reflected by the concave reflection surface, this noise silencer may not sufficiently reduce noise in a relatively wide frequency range.